A resilient seal of the O-ring type has proven to be a very effective sealing medium in a number of valves, including gate valves and ball valves. In sealing, the pressure of the fluid acting against the seal ring is transmitted through the resilient material thereof to form a pressure seal against the opposing working surface. However, when the valve is initially moved to its open position there is a tendency for the seal ring to maintain its seal and follow the opposing working surface as it is moved away from the groove in which the seal ring is carried. This, coupled with the force of the initial jet of high pressure fluid, has a tendency to dislodge the seal from the groove in which it is normally carried. Various venting means and structural provisions have been devised to prevent seal ring dislodgement and, among them, are the provision of restraining lips at the opening of the seal ring groove and the use of relatively hard materials in the seal ring itself. The restraining lips with the hard material are effective in reducing the liklihood of seal ring dislodgement but, by the same token, make seal ring installation during manufacturing and servicing much more difficult. Accordingly, the seat rings in which the seal rings are carried are generally formed as a two-piece assembly whereby the seal ring may be placed over the inner seat ring and the outer seat ring mounted over the installed seal ring and inner seat ring. However, the machining and precise finishing of two seat ring components for assembly render manufacturing costs execessive and it is highly desirable to have one-piece seat ring in which a seal of the O-ring type may be installed.